1) Resilience:
People tend to miss out in this; you must remember that elemental shamans are a tanking class in arenas. From my Point of View, I would never advice anyone use under 1.150. It’s such a brilliant stat for survival, and it decreases the chance of you becoming a viable target. Besides, you already have roots, thunderstorm, frost shock, and peels from your other teammate. Mostly I cannot think of any situation where I would gimp myself to lower the resilience, or well – Only chance would be in some spell cleave where you will mostly never become the target, but it’s quite unusual.

2) Spell power:
Self explanatory, more spell power means more damage. On top of resilience spell power is the most important stat for an elemental shaman. More constant damage basically, you can never go wrong with it really, and the more damage you are doing, the more pressure you are applying onto the opponent healers, and they are more likely to put themselves in a bad position or eat a good interruption.

3) Haste:
This is the stat a lot of people misunderstand as an elemental shaman, it’s probably the best stat as far as spell caster goes, however how much is it you should & wish to aim for with this stat?
Haste is a confusing stat but it's best described as the stat that "makes your actions faster". The effect of haste is essentially "to do more per unit of time". For a caster that means "cast more spells per unit of time". Well if we're going to cast more spells in the same amount of time, that means each spellcast takes less time.

Sources of Haste
How to calculate haste can also be confusing because of the math involved. Different sources of haste stack multiplicatively. Here's the most common sources of haste for an elemental shaman:

Calculating Casting Time
Once the total effective haste number is known, the next thing we care about is "how must faster does that make me?" The "hasted cast time" of a spell is equal to the base cast time (AFTER talents) divided by your effective haste. Again, let's look at some examples:

One thing to note is that the cast time reduction of buffs is less at higher amounts of haste. Note above that bloodlust at 0 haste rating reduced the lightning bolt cast time 0.462 seconds. But with 500 haste rating already in place, bloodlust only provides an additional reduction of 0.4 seconds. This gives the appearance that "haste has diminishing returns" which is not really true. The 30% more haste from bloodlust makes you 30% faster whether you have 0 haste rating or 1000 haste rating. However it is generally accepted that the 30% haste from bloodlust is "more valuable" to someone with 0 haste than it is to someone with 1000 haste.

Haste Caps and the GCD
While there are various "soft caps" to haste, there is no absolute cap and cast times continue to reduce indefinitely. If you could achieve 10,000 haste rating, you would cast lightning bolts in 0.494 seconds. HOWEVER, there IS a cap on the GCD. The GCD cannot be reduced below 1.0 seconds. So in the example above where Lava Burst's cast time is 0.75 seconds, you would have to wait 0.25 seconds after the Lava Burst before you could cast another spell...this is because the GCD would still be 1.0 seconds. In a PVP setting, it can still be advantageous to push spells below this 1.0 threshold though since the shorter cast times are still more difficult to interrupt and you can also start moving again sooner.

As for the GCD, it is reduced by haste the same as a spells. You can calculate it just like a spell with a 1.5 second base cast time. So the cast time of your Chain Lightning or your Lava Burst is the same as the time of the GCD...just don't forget the minimum of 1.0s. If your CL is showing as 0.8, it will be 0.8 but the GCD will still be 1.0.

Thanks to Vyrolan from Garona (us server)

4) Hit rating and spell penetration:
This one is a bit tricky; it’s probably the most important stats as far as meeting top teams goes.
When you’re playing a top team you really don’t want any shocks to be resisted, nor do you want spells to be missed totally, since they may very well lose the game for you.

Before I go in depth I just wish to remind you that we’re playing this game World of Warcraft, the king of RNG.

Hit:
In general the different 2% racials are total ass and that can any top player agree on, but the stats you want to aim for is 4% hit as for any caster. It’s the hit cap in PvP without the 2% racials which you can’t really do much about.

Spell penetration:
This stat is as important as hit, I would say anything above 125. Yes, I obviously know people claim they are doing fine without this high number, and I respect others having a different opinion, this is just our conclusion:

Why is it, you take elemental shamans into arena, since it’s not only our good damage, but purges and shocks as well. However, the most important ability is purge, which scales with spell penetration. You just don’t want it to be resisted against anything, again against top teams you just don’t have time to depend on stuff like that. Overkill or not you decide, but I would recommend least 125 spell penetration to be on the safe side.

5) Crit and stamina:
I won’t go with a lot of facts and stuff here, as long as you remain 30%+ in crit & 25k unbuffed in health, you will do just fine. If you just gear proper you don’t have to think about these stats at all, it comes natural with the best gear setup you will be running as a competitive elemental shaman.

Now that I’ve walked through the most important stats let’s look on how you want to gear, when people ask me in-game I tend to just tell them to check my armory. I’ll be listing the best gear you’ll be able to get in s8. Both PvE oriented and PvP, just remember that elemental shaman isn’t a class which you want to abuse PvE gear with too much. It’s pretty straight forward really.

With that being said, let’s go on checking how you can gear.
http://chardev.org/?profile=387561 Fully PvP, nothing more to add to it really
http://chardev.org/?profile=429031 Best PvE gear abused, if you got access to this you should use it without a doubt. Rotface trinket is beyond op at the moment.